The present invention relates to the field of sealing systems, particularly internal seal systems for coaxial cables. The preferred seal systems are particularly well suited for use in difficult environments wherein it is desirable to seal inside a coaxial cable without the normal means available such as O-rings in machined grooves, metal o-rings, or a split metallic ring. One such application is in data transmission systems for downhole environments, such as along a drill string used in oil and gas exploration or along the casings and other equipment used in oil and gas production.
The goal of accessing data from a drill string has been expressed for more than half a century. As exploration and drilling technology has improved, this goal has become more important in the industry for successful oil, gas, and geothermal well exploration and production. For example, to take advantage of the several advances in the design of various tools and techniques for oil and gas exploration, it would be beneficial to have real time data such as temperature, pressure, inclination, salinity, etc. Several attempts have been made to devise a successful system for accessing such drill string data. One such system is disclosed in co-pending U.S. application Ser. No. 09/909,469, now U.S. Pat. No. 6,717,501 which is commonly assigned with the present invention and also incorporated herein by reference herein. Another such system is disclosed in co-pending U.S. application Ser. No. 10/358,099 the title of which is DATA TRANSMISSON SYSTEM FOR A DOWNHOLE COMPONENT file on Feb. 3, 2003. The disclosure of this U.S. application Ser. No. 10/358,099 is herein incorporated by reference.
Downhole data transmission systems use seals to protect the electrical transmission line from the drilling environment such as the system described above. Drilling fluids such as drilling mud are pumped down the center of a drilling tool for many purposes such as to flush out cuttings on the bottom of the borehole. Drilling fluids are often corrosive which increases the difficulty of making a successful seal. A borehole created by drilling can have various temperature and pressure ranges as the depth of the borehole increases. Due to the large range and subsequent combinations of temperatures and pressures along the depth of the borehole, a robust seal design is necessary to protect the electrical transmission line of a data transmission system.